1. Field of the Invention
The present invention relates to a compression ignition type engine.
2. Description of the Related Art
In the prior art, it is known to arrange an exhaust gas purification catalyst in an engine exhaust passage for purifying components included in an exhaust gas discharged from the engine. There is a minimum temperature for the catalyst to activate and to begin the action of purification of the catalyst. Normally, the temperature of the catalyst is increased to the activation temperature by the exhaust gas flowing into the catalyst. However, the temperature of the exhaust gas may be low depending on the engine operation state and, in this state, the temperature of the catalyst may be lower than the activation temperature. To solve this problem, a method is disclosed in the Japanese Unexamined Patent Publication No. 5-328528, for increasing the temperature of the catalyst to above the activation temperature in the above state.
In this Publication, for example, when the operation of the engine starts and it is presumed that the temperature of the exhaust gas is low, the engine is operated at twice the normal engine speed to increase the temperature of the exhaust gas, thereby increasing the temperature of the catalyst to the activation temperature.
In the case that the temperature of the catalyst is increased as explained above, it is necessary to operate the engine at twice the normal engine speed, and therefore, the fuel consumption of the engine becomes large. To solve this problem, in the above mentioned Publication, when the engine is operated at the high engine speed, an electric motor is driven as a generator by the output of the engine to store the excess output as electric power. The electric power is used to supplement the output of the engine, depending on the circumstances.
However, when the excess output of the engine is converted to the electric power by the electric motor serving as a generator, the fuel consumption of the engine at least becomes large because the conversion ratio is not 100 percent.
An object of the present invention is to prevent the fuel consumption of the engine from becoming large while maintaining the exhaust gas purification catalyst in the activated state.
To accomplish the object of the present invention, in the first invention, there is provided a compression ignition type engine wherein, when an amount of an inert gas in a combustion chamber becomes large, an amount of generation of soot gradually increases to a peak, and when the amount of the inert gas in the combustion chamber becomes even larger, a temperature of fuel and a temperature of a gas around the fuel at a combustion of the fuel in the combustion chamber becomes lower than a temperature which soot is generated, and thus, almost no soot is generated, comprising; means for selectively performing a first combustion mode in which the amount of the inert gas in the combustion chamber is larger than that of the inert gas in which the amount of generation of the soot is a peak, and a second combustion mode in which the amount of the inert gas in the combustion chamber is smaller than that in which the amount of generation of the soot is a peak; an exhaust gas purification catalyst arranged in an engine exhaust passage for purifying components included in an exhaust gas; an electric motor for outputting an output separated from the output of the engine, when the engine is operated such that the engine outputs a value of the output determined on the basis of the engine operation state, the output of the electric motor supplementing the shortage of the output of the engine relative to the requested output; and means for selectively performing a first control to operate the engine such that the engine outputs an output larger than the value of the output determined on the basis of the engine operation state, and a second control to operate the engine under the first combustion mode; wherein when the temperature of the exhaust gas purification catalyst should be increased, one of the first and second controls is performed on the basis of a predetermined conditions.
In the second invention according to claim 2, the engine further comprises a battery, and when the output of the engine is larger than the value of the output determined on the basis of the engine operation state, the electric motor is driven as a generator by the output of the engine to store the output of the engine in the battery as an electric power, and when the temperature of the exhaust gas purification catalyst should be increased and the amount of charged electric power in the battery is smaller than a requested amount, the first control is performed, and on the other hand, when the temperature of the exhaust gas purification catalyst should be increased and the amount of charged electric power in the battery is larger than the requested amount, the second control is performed.
In the third invention according to claim 1, the exhaust gas purification catalyst has a NOx catalyst for purifying the NOx included in the exhaust gas.
In the fourth invention according to claim 2, the NOx catalyst has a NOx absorbent which absorbs the NOx included in the exhaust gas when the air fuel ratio of the exhaust gas flowing into the catalyst is lean and releases the absorbed NOx therefrom when the air fuel ratio of the exhaust gas flowing into the catalyst becomes one of the stoichiometric air fuel ratio and a rich air fuel ratio.
In the fifth invention according to claim 1, it is judged that the temperature of the exhaust gas purification catalyst should be increased when the temperature of the exhaust gas purification catalyst is lower than a temperature in which the catalyst is activated to purify the components included in the exhaust gas.